__getattr__ called when an attribute lookup has not found the attribute in
the usual places. __getattribute__ called for all attributes.
cdn_url now return CDNFile instance — chainable interface for can methods.
All methods from https://uploadcare.com/documentation/reference/basic/cdn.html
are implemented.
Tests for CDNFile.
Templates filters for CDNFile.
Tests for template filters.
Registration of additional namespaced version for every template filter.
Merge pull request #27 from homm/chained-cdn-url

Chained cdn url